I removed the scripts that preceded TweenMax except for jquery and it made no difference. I was able to dig into it a little further and discovered that it's not the removeChild that's failing, it's an appendChild that precedes it.
I checked the number of children in the element and then stepped over the appendChild. When I check the number of children after, it hasn't changed. I changed the call to insertBefore(k, z.firstChild) and it worked. Someone, somewhere must be overriding appendChild.
By the way, the failing function is only called for IE8.
It's working now, but it's a work around.